This invention relates to a method and means for producing semi-conductor devices and more particularily, to improvements in solid state epitaxially grown semiconductor devices.
In a U.S. Pat. No. 3,413,157, there is described a solid state epitaxial growth aluminum doped silicon by migration of a silicon through an aluminum thin film. A silicon surface is provided having a silicon dioxide layer thereover through which holes are etched to provide access to the silicon surface. A layer of aluminum is applied to cover the silicon dioxide surface as well as the holes therethrough. A layer of silicon is provided over the layer of aluminum. Another layer of aluminum is then provided over the silicon layer. The last aluminum layer is a contact layer. The substrate and the layers thereon are heated to approximately 565.degree., which is a temperature below the aluminum eutectic temperature, for a period of time, during which silicon will migrate through the evaporated aluminum layer and grow on the surface of the underlying silicon, through the holes, as an epitaxial layer. The solid state grown silicon layer will be doped to the maximum solubility of aluminum and silicon because of the dissolving of the aluminum into the silicon.
Other known techniques for growing doped layers, usually have a density gradient of impurity concentration with a maximum concentration at the surfaces decreasing with the distance from the surface. In the method described, there is no impurity gradient the doping being uniform throughout the grown layer.
A limitation upon this patented technique is that the epitaxially grown layer is always doped with the metal through which the growth takes place, which in the patented system is aluminum. If it were possible to grow an epitaxial layer in which an epitaxial layer is free of dopants or in which a dopant may be selected to provide a semi-conductor with desired properties, a much more flexible and useful arrangement would be possible. Also, it may be desirable to have a layer which is not saturated with a dopant.